Globally, 11 out of 12 years (from 1995 to 2006) rank among the 12 warmest years on record since 1850

Enough evidence of long-term changes such as rising temperatures which point to climate change, says CSE

New Delhi, April 12, 2010: The summer of 2010 has just begun, and India is already reeling under extreme temperatures as the mercury climbs unprecedented heights. In fact, the India Meteorological Department (IMD) has said that Delhi has been experiencing its second warmest March since 1901, the year when systematic record-keeping began.

According to Centre for Science and Environment (CSE), there is enough scientific evidence of long-term changes – including temperature increases -- happening not only in India, but across the world, which suggest the influence of climate change.

Mercury rising

On April 11, Delhi recorded its hottest day this year when the maximum climbed up to 41.6°C, six degrees above normal. The minimum also touched the highest at 24.4°C, four degrees above normal. The IMD has predicted that heat wave conditions will continue over north India for entire April.

In March, the mean maximum and minimum temperatures were 33.8°C and 18.6°C, respectively – again, far higher than the average normal of 30°C and 15.4°C, making it the second warmest March since 1901 next only to the month of March in 1953.

The unusually high temperatures this year are in line with the overall warming trends of the last decade. According to the data of the IMD, 2009 was the hottest year ever recorded for India. The mean annual temperature stood at 25.55°C, almost a degree above the normal. Globally too, the year 2009 was the second warmest year ever recorded, according to the National Aeronautics and Space Administration (NASA) of the US.

In fact, the decade of 2000-2009 has been warmest ever, points out NASA. It also says 2005 was the warmest year ever recorded since systematic data collection began. According to the IMD, eight of the 12 hottest years since 1901 were during the last decade. Temperatures in India are, naturally, following the overall global trends.

Greater the CO2 concentration, higher the temperature

What do the rising mercury graphs imply? In a recent study titled Surface air temperature variability over India during 1901-2007 and its association with ENSO, K Krishna Kumar, senior scientist at the Indian Institute of Tropical Meteorology (IITM), Pune, and D R Kothawale and A A Munot -- both scientists at IITM – have reported that during the period 1901 to 2007, the all India mean temperature had gone up by 0.51°C in every 100 years. The maximum and minimum temperatures for the same period had gone up by 0.71°C and 0.27°C per 100 years. The study also found that the increase had been higher since 1970.

When seen alongside the Intergovernmental Panel on Climate Change’s (IPCC) Assessment Report 4, this higher increase in temperature since 1970 corresponds with the accelerated increase in atmospheric concentration of CO2: the IPCC estimated that CO2 concentration has increased globally by about 103 ppm since pre-industrial times. The first 50 ppm increase above the pre-industrial value was reached in the 1970s after more than 200 years, whereas the second 50 ppm was achieved in about 30 years, pointing to an increase in emission intensity.

The IPCC Report also says that global mean surface temperatures had risen by 0.74°C ± 0.18°C over the period 1906–2005. In the period 1955-2005, the rate of warming was almost double than the 100-year average.

In March 2009, a meeting of more than 200 scientists at Copenhagen warned that the IPCC’s assessment of climate warming was, in fact, quite conservative – they averred that greenhouse gas emissions and many aspects of the climate are changing closer to the upper boundary of the IPCC’s range of projections.

Other studies point to similar trends. In a study published in Current Science on September 25, 2007 S K Dash, an atmospheric scientist at IIT-Delhi, compiled temperature data of 102 years (1901-2003). He reported that the minimum temperature (recorded during night) in winter in the northern part of the country increased 0.7°C while in the south, it increased by 0.3°C in 102 years. Most of this change has occurred over the last three decades, in which period atmospheric carbon dioxide concentrations have also gone up considerably.

Dash had also analysed the changes in maximum and minimum temperatures in different zones in the country in the last century. His findings:

In north-central India, the maximum temperature has gone up by 0.8°C and the minimum by 0.2°C.

In the peninsular region, the maximum and minimum temperatures have gone up by 0.5°C.

In western Himalaya, the maximum temperature has gone up by 0.9°C and the minimum by 0.5°C.

In north-east India, the maximum temperature has gone up by 1°C and the minimum by 0.2°C.

In north-west India, the maximum temperature has risen by 0.6°C, while the minimum has gone down by 0.2°C.

On the west coast, the maximum temperature has gone up by 1.2°C and the minimum by 0.4°C.

In the eastern coastal region, the maximum temperature has gone up by 0.6°C and the minimum by 0.2°C.

According to a study based on IMD data, the all-India annual mean temperature has increased by 0.5°C in the period 1901-2003. The rise in minimum temperature in the winter and post-monsoon seasons is 0.4°C and 0.7°C, respectively.

Another study, done by the IMD, shows that over the last 100 years during the summer months of March and April, the mean temperatures have increased by 0.76°C and 0.58°C, respectively.